Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $243.44   8.645%   $264.4854   $264.49   $264.50   $264.50  
  Purchase #2 $78.35   12.552%   $88.1845   $88.18   $88.20   $88.20  
  Purchase #3 $69.87   6.233%   $74.225   $74.23   $74.25   $74.20  
  Purchase #4 $113.26   7.551%   $121.8123   $121.81   $121.80   $121.80  
  Purchase #5 $175.67   5.408%   $185.1702   $185.17   $185.15   $185.20  
  Purchase #6 $242.73   5.434%   $255.9199   $255.92   $255.90   $255.90  
  Purchase #7 $31.63   12.362%   $35.5401   $35.54   $35.55   $35.50  
  7 purchase totals = $954.95       $1,025.3374   $1,025.34   $1,025.35   $1,025.30